Insulator and method of manufacturing same



Patented Mar. 9, 1948 INSULATOR AND METHOD OF MANUFACTURING SAME Davidge H. Rowland, Brighton, N. Y., assignor to The Porcelain Insulator Corporation, Lima, N. Y., a corporation of New York No Drawing. Application December 5, 1945, Serial No. 633,041

2 Claims. 1

This invention relates to a wet process porcelain insulator and method of making the same, and has for its purpose to increase the density and improve the electrical and mechanical strength of such insulators, speed up production. reduce losses due to imperfect insulators, and thus lessen the cost of manufacture very materially.

In the manufacture of wet process porcelain insulators, a chief source of loss and increased cost has been due to what is known as swell bloat resulting from the' gases created during firing which fill the voids left by the water in the insulator body and fracture the voids or cell structure if subjected to excessive firing temperatures. This causes a lowered density and efficiency of the porcelain and a pitted formation and appearance of the glazed surface, necessitating discarding many such units.

According to previous methods, if insulators are not fired at sufilciently high temperatures, the voids left by the water on drying do not seal off but remain connected by interstices, and as a consequence the insulator body is porous, absorbent, and unsatisfactory for high voltage service exposed to weather, while firing at too high temperatures causes expansion of the gases and rupture of the voids or cells, resulting in bloating or swelling and surface pitting.

It has been essential therefore to maintain the firing temperature closely in a narrow range around 2340 F. with a variation of not more than 40, and when properly fired, the voids seal off and the porcelain body includes a mass of small cells or voids filled with a combination of rarefied gases. A slight overfiring causes the gases in the voids to exert pressure and when some of the oxides and molten salts decompose and form more gas, there is produced an increased internal force that ruptures the voids or cells and produces bloat or swelling. The effect of this can be seen in pits on the glazed surface of the porcelain, and further increase in firing temperature causes rapid swelling of the porcelain and a correspondingly rapid decrease in density.

It is difficult and practically impossible to control and maintain the temperatures always within a safe firing range, above the point at which the porcelain body is underfired and becomes soft-like or liquid-absorbent to an extent that it will take dye, and under the point at which the insulators are overfired and the gasfilled cells fractured with consequent swelling. To obtain perfect insulators, it has been necessary to fire the insulators so slowly that the heat will penetrate to the interior of the porcelain body without excessive heat at the surface that will cause bloat and pitting of the glazed exterior.

This requires that insulators of large size be fired much more slowly than small insulators because of the greater length of time required for the heat to penetrate a large wet clay body, and since insulators of all sizes are fired in a kiln at the same time, a temperature must be maintained at such a point as not to damage the largest size units and the firing time on the small insulators is necessarily slowed to maintain the largest insulators within a safe firing range. This is uneconomical because thick and thin pieces are necessarily fired at the same time, and the greater the temperature range, the easier it is to produce high quality, efficient insulators of density in various sizes.

As a result of this condition, a large percentage of insulators as they come from the kiln will not pass inspection but must be discarded because unfit for sale, resulting in substantial loss and increased cost of production. In addition, many insulators which do not exhibit the characteristic surface pitting due to swell bloat have been subjected to excessive heat in the kiln so that their interior structure is not of uniform density and they possess such porosity as to render them more susceptible to dielectric and mechanical overloads than if fired within the proper temperature range.

The present invention is designed to overcome these objections in the manufacture of wet process porcelain insulators, to reduce losses and cut down manufacturing costs by increasing production, and to produce insulators characterized by greater dielectric and mechanical strength by introducing into the mix before firing a material that effectively prevents swelling or bloat, irrespective of the temperatures to which the insulators are subjected, and thus produce an insulator structure of uniform density and with a smooth, unpitted, and perfectly glazed exterior surface.

As a result of the material introduced into the clay mix, which combines with the gases in the voids to form stable compounds, reduce gas pressure, and prevent fracture of the gas-filled cellular structures and consequent swelling, it is possible by fixation of the gases to employ higher temperatures in the kiln, and therefore increase production by firing large insulator bodies more quickly without adversely affecting the smaller and therefore characterized by greater strength to resist both electrical and mechanical strains.

According to one practical application of the invention, there is employed a mix composed of approximately 26% English ball clay, 20% fiint, 32% feldspar, and 22% china clay, and to this mixture is added, before shaping and firing the clay bodies, an amount of aluminurn or other suitable metal in finely divided or powdered form amounting to approximately 1% by weight of the total dry mix.

The aluminum or metal is preferably in a finely divided state that can be passed through a G- mesh U. S. standard sieve, although finer particles or somewhat coarser particles may be successfully used to attain the desired purpose. After the clay mix containing the finely divided aluminum is moistened and shaped in accord with usual practices, the clay pieces are placed in a kiln and fired within a range from a normal firing temperature of approximately 2340" F. up to 2450 or even higher without causing swelling either at the surface or in the interior of the insulator bodies, whereas insulators made without powdered aluminum in the mix are aifected by pufiing or swelling if fired at a temperature much above 2340 F.

When the wet clay is fired and oxides decomposed under the high temperatures, oxygen, nitrogen, and other gases are thrown off, and the powdered aluminum combines with these gases forming stable oxides, nitrides, and other stable substances, avoiding gas pressure in the voids or cells of the insulator body that would otherwise cause fracture and bloat if fired under excessively high temperatures.

Reaction between the powdered aluminum and the released gases causes a fixation of the gases, and by preventing destructive action on the porcelain, increases the firing rang-e from 40 F., -according to previous methods, to as much as 120 F. or more.

A standard Wet process porcelain insulator when properly fired has a specific gravity of 2.38, and when two porcelain bodies, one including 1% of powdered aluminum in the mix and the other without any aluminum, were fired to cone l3 or approximately 2450 F., it was found that the porcelain without the aluminum content had a specific gravity of 1.67 making it unsuitable for commercial purposes, whereas the porcelain containing the aluminum powder had a specific gravity of 2.38.

Insulators made according to the invention show a smoother and more perfectly glazed surface than insulators as heretofore constructed without powdered aluminum in the mix, and it is now possible to produce insulators of high quality standards within a wide firing range. Since firing represents about 30% of the total cost of insulator production, by making it possible to employ higher temperatures and to this extent decreasing the firing time, a material saving in cost is assured. The surface of the insulator is not subject to pitting which frequently results from bloating or swelling, it is possible to obtain a more perfectly glazed surface, and the interior structure of the porcelain body is correspondingly denser and more uniform throughout, owing to the absorption of the gases produced on firing and the consequent elimination of undue expansion of the gases when heated.

Such an insulator can be fired and produced much more rapidly than heretofore since the maximum temperature required to drive the heat quickly to the interior of a large body of porcelain can be employed without damageto the exterior surface of the insulator or to the pore tions near the surface, and moreover the insulator possesses a density that is uniform throughout. Such insulators will standany of the-di'-- v electric or mechanical strains that are normally encountered in service and are better qualified to resist thermal shocks to which they are likely to be subjected than insulators characterized by a variation in density inthe heavier sections due to the practical difiiculties in simultaneously heating many porcelain units of different sizes evenly throughout or maintaining a safe firing range.

While the invention has been described with reference to a specific construction and procedure, it is not confined to the details herein disclosed, and this application is intended to cover such modifications or departures as may come Within the purposes of the invention and the scope of the following claims.

I claim:

' 1. The method of making vitreous wet process porcelain insulators which consists in forming a mix of approximately 26% ball clay, 20% flint, 32% feldspar, 22% china clay, and aluminum in finely divided form in the approximate amount of 1% by dry weight of the mix, moistening the mix and shaping the insulators therefrom, and thereafter firing the shaped insulators at temperatures ranging between approximately 2340" F. and 2450 F. i

2. An insulator constructedg-according to the method of claim 1. p DAVIDGE H. ROWLAND.

EEFERENGES CETED The following references are of record in the file of this patent: I

FOREIGN PATENTS France 191i 

